1. Field of the Invention
The invention relates to a coupling device for a tube comprising a coupling piece with an insert end for the tube and a sealing organ which is suitable for realizing a seal around the tube inserted in the coupling piece, whereby the sealing organ comprises a series of elements which together form a ring enclosing the tube, and whereby the elements have been provided with at least one grip ring, extending over at least a part of the circumference of the tube. Further the invention relates to a method for manufacturing a grip ring for such a coupling device.
2. Description of Related Art
Such a coupling device is known from the European patent application EP-A 0 794 378 of applicant. The known coupling device is applied with tubes of steel, stainless steel, eternite, cast iron, coated steel, PVC, polyethylene and asbestos cement and will be used as connection for one or two of such tubes. On the one hand it is then important that the coupling device provides an adequate sealing and on the other hand that this sealing is capable to resist tension strains. This last function is provided by the grip ring which is part of the known coupling device.
It is known from the Dutch patent application 1009 734 of applicant to embody the grip ring with dents that are pressed out of the surface of the grip ring. The dents border each time at one side on the slit-formed cut-aways that are punched out from the grip ring. A problem of the known grip ring which is part of such a coupling device, is that with the application of the coupling device on tubes which have been manufactured with softer material, the grip ring seems to operate as a cheese slicer, so that the tensile strength of the coupling device according to the known state of the art is relatively limited. When the coupling device according to the state of art is applied with such softer materials as polyethylene, polybutene, acrylbutadienestyrene, or polypropylene, a tensile strength results which for the large diameter-sizes measures approximate 6 to 7 bar, and for the smaller diameter-sizes can be measured at 15 to 16 bar.
It is known from the Dutch patent application 1 014 758 of applicant to embody the grip ring with projections that substantially radially inwardly extend away from the surface of the grip ring. It is proven that the coupling device provided with this grip ring as applied to a tube of relatively soft material with a diameter of 200 mm, tolerates a tension strain of 25 to 30 bar.
From U.S. Pat. No. 6,499,771 a coupling device according to the introduction is known whereby projections pressed out of the surface of the grip ring are applied, which have been provided with anchor teeth extending in the plane of these projections. These known anchor teeth serve to resist axial rotation of the clamped tube.